Also, handle first user differently under the hood

cmd/view/users.go

@@ -236,12 +236,18 @@ func AddFirstUser(c *control.CliArgs, db *model.DB, s *control.CookieStore) http
 			return
 		}
 
-		htmlData.ID, err = db.AddUser(htmlData.User, pass)
+		htmlData.ID, err = db.AddFirstUser(htmlData.User, pass)
 		if err != nil {
 			log.Println(err)
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}
+		if htmlData.ID > 1 {
+			errString := "error: there is already a first user"
+			log.Println(errString)
+			http.Error(w, errString, http.StatusInternalServerError)
+			return
+		}
 
 		if err := saveSession(w, r, s, htmlData.User); err != nil {
 			log.Println(err)